In essence, a vacuum is a volume of space that is void of any matter such that the gaseous pressure of this volume of space is less than standard atmospheric pressure. Simply measuring the vacuum in a fluid is neither new nor novel, and the methods to do so do not need to be mentioned in this application, except to say that these prior methods, when applied to a living system, have generally been invasive in nature and therefore at times were susceptible to cross contamination of the fluids in which the vacuum is being measured. Thus, there exists a need in the art, especially in the area of ophthalmic instruments such as Phacoemulsification machines, for a more hygienic and noninvasive system to measure fluid in a vacuum.
Phacoemulsification machines are used for removing cataracts, or crystalline manifestations, from the eye. The machine may include a probing device, which typically constitutes an ultrasound driven hollow needle. In such a case, the needle is inserted into the eye through a small incision in the opaque layer of tissue surrounding the pupil, and vibrates at ultrasonic frequency to emulsify any crystalline manifestations that may be present. The emulsified particles of cataract are then aspirated through an opening at the tip of the hollow needle. The aspiration process is, in a sense, two interconnected operations. The first operation of the process is the actual removal of the cataract fragmentations through the application of a vacuum pressure. During the removal of the fragmentations, there must be a continuous circulation of fluid through the eye. This is provided by the second operation, in which the hollow needle supplies this circulation of fluid.
The entire process is a delicate one, as the pressure in the eye must be constantly measured and maintained to prevent a number of problems. For example, during the removal operation, any blockage in the hollow needle, possibly created during the passage of one cataract fragmentation, may cause a void, or vacuum, to build in said needle. In such an instance, it may be necessary to apply a higher level of pressure in order to dislodge the blockage. Failure to adequately measure and control the fluid pressure during this process may result in the sudden ejection of the blockage followed by a rapid influx of fluid from the eye into the void. If this fluid is not replaced with sufficient speed, it could lead to the subsequent collapse of the eye chamber. Another way to remove a blockage from the hollow needle is to reverse the flow of fluid in the needle to expel the blocking fragmentation. Again, however, if the fluid pressure is not adequately measured and controlled, the ramifications could be extremely problematic. In this situation, the vacuum pressure would be negative, so when the blockage is removed there may be a subsequent flooding of the eye chamber leading to an inflation of the eye. Furthermore, as discussed above, the use of a standard pressure measuring system to monitor these pressures is not an adequate solution to the problem, as cross contamination of fluids will then become an issue.
The industry has devised a number of different systems in trying to fulfill this need for a non-invasive system of measuring vacuum in a fluid, both respective and irrespective of use with Phacoemulsification machines. However, all of these solutions have been shown to suffer from deficiencies when utilized in this application. One such system involves separating the measured fluid from another fluid, usually air or gel, with a membrane, and measuring the pressure in the other fluid. Another such system involves using an elastic element to load a force transducer, for example, pressing a tube that contained the measured fluid to a force sensor and measuring the fluid pulling force on that element using the differences between the zero atmospheric level and the vacuum level. The two aforementioned systems, though operable, suffer from increased levels of hysteresis (path dependence) and volume variance. A third method uses a diaphragm exposed on one side to the fluid and on the other side to a force transducer. The pulling force on the diaphragm is measured usually using a magnetic coupling between the diaphragm and the force sensor. However, this third system can suffer from being overly robust in construction. Thus, there still exists a need in the art for a simply constructed, noninvasive system for the measuring of vacuum pressure in a fluid that will not suffer from high levels of hysteresis or volume variance.